1. Field of the Invention
The present invention relates to electrical cables and more particularly, to electrical cables and shielding tapes therefor having parallel serpentine pattern adhesive strips thereon for securing the shielding tape to and around conducting and insulating elements within the cables.
2. Description of the Prior Art
Electrical cables are well known in the electronics industry. They generally comprise an electrical conducting element, e.g. a copper wire, surrounded by a dielectric element or an insulator, which in turn is covered by a metallic shield. Around the shield is a conductive braid, followed by an outer protective coating or jacket.
In order to bind the metallic shield to the insulating element, those skilled in the art generally use adhesives. These adhesives also function to prevent the introduction of moisture into the enclosed conducting and insulating elements which can corrode and short circuit the cable. If properly applied, the adhesive also enables the metal in the shield's upper surface and its lower surface to contact when the shield is wrapped around the insulating element so that its two ends overlap. Such metal-to-metal contact is necessary to prevent or reduce electrical or electromagnetic interference in the electrical cable system.
Several means for preventing such undesirable effects in the electrical cable have previously been proposed. For example, U.S. Pat. No. 4,746,767 discloses a metal foil shielding tape having a plurality of square-shaped exposed metal contact pads defined in rows and columns in a checkerboard pattern by an adhesive. When positioned around an insulator in a cable, a top side of the shielding tape overlaps with a bottom side of such tape and the adhesive connects both the insulating member and the lower surface of the shielding tape to the shielding upper surface of the shielding tape. However, under the disclosed arrangement of contact pads and adhesive, the size of the barrier to electrical or electromagnetic interference is limited.
In practice, the coated surface of the prior art tape covers 75% of the surface of the foil and the uncoated pads cover the remaining 25% of the surface area. Where greater metal-to-metal contact is desired, the uncoated area may be increased; but at best, the contact pads of such prior art tapes may only cover fifty percent of the total surface area. This is because any greater uncoated area would result in localized or isolated, noncontiguous adhesive pads which cannot assure against moisture penetration. If the metal-to-metal contact of the upper and lower surface of the shield tape could be increased in the overlapping areas while maintaining the moisture-retardant effect of the adhesive, a more effective shield will result.
The disadvantages of the prior art are overcome by the present invention which achieves a greater metal-to-metal contact area because of a greater amount of uncoated material in a shielding tape for an electrical cable with a minimal amount of overlap between one side of the shielding tape and the other side. This is achieved by the application of a series of parallel serpentine shaped strips of adhesive onto one surface of a metal shielding tape to form a unique and particularly advantageous bonding pattern.